High power pulse type modulator employing vacuum tube to divert current for ignitrondeionization



Feb. 19, 1963 c. THEODORE 3,078,418 HIGH POWER PULSE TYPE MODULATOR EMPLOYING VACUUM TUBE To DIVERT CURRENT FOR IGNITION DEIONIZATION Filed Jan. 23, 1961 FIG. 1.

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CHARLES THEODORE AGENT nite tates Deiaware Filed Jan. 23, 1961, Ser. No. 84,126 7 Claims. (Cl. 328--67) My invention relates to an electrical pulse type modulator of high power capability and particularly to such a device employing a high vacuum tube for current diversion.

The need for higher and higher power short pulse type modulators constantly increases as higher power oscillator vacuum tubes become available. In order to produce pulses in the hundred megawatt class a gaseous switch tube of the nature of an ignitron is required. While these tubes have numerous advantages in handling high power, it is necessary that the anode voltage of the same be Withheld after a discharge for a period of the order of 150 microseconds in order that the switch tube may deionize.

The prior art, at lower power levels than I have achieved, has been able to employ hydrogen thyratrons to withhold the anode voltage from the switch tube in order to accomplish deonization. It is not satisfactory to attempt to operate hydrogen t-hyratrons in parallel in order to obtain increased current-carrying capability and single tubes to carry the current I require have not been produced by man, and may not be producible.

I have found that by employing a high vacuum diode in place of the hydrogen thyratron and by adding a high vacuum triode for diverting current from the diode for the period of time required for deionization of the switch tube I have been able to increase the power capabilities of a pulse type modulator almost without limit and to obtain long life from the essential elements of the modulator because of the high vacuum nature thereof.

Specifically, I provide a high power triode with the anode thereof connected to the junction between the charging inductor and the anode of the diode and supply a positive pulse to the grid of the triode for the period of time required for deionization of the switch tube. The triode drains off the current flowing through the inductor and maintains the voltage at the anode of the switch tube at essentially zero volts.

An object of my invention is to provide a high power line type modulator.

Another object is to provide a deionization facility for a gaseous type switch tube.

Another object is to provide high vacuum means for removing voltage from a gaseous tube to allow the latter to deionize.

Another object is to provide a modulator circuit having long life and high reliability.

Other objects will become apparent upon reading the following detailed specification and upon examining the accompanying drawing, in which are set forth by way of illustration and example certain embodiments of my invention.

FIG. 1 shows a schematic diagram of my invention, and

FIG. 2 shows certain waveforms explanatory thereof.

In FIG. 1 V is a high vacuum triode characteristic of my invention. Similarly, V is a high vacuum diode. V is typically an ignitron; that is, a high power mercury vapor tube having a pool of metallic mercury for a cathode. V is illustrative of an electronic load, such as a high power klystron.

High voltage source 1 is typically one supplying electric power of the order of ten amperes at eighteen-' atent O ice thousand volts (=18 kv.). This source connects through inductor 2 to the anodes of both V and V The cathode of diode V connects to the charging artificial transmission line generally indicated at 3 and composed of a number of series-connected inductors 4 and shunt capacitors 5. In an illustrative embodiment the individual inductors of the transmission line have an inductance of the order of less than one microhenry and each capacitor a capacitance of the order of five one-hundredths of a microfarad. More sections of the line are normally employed than have been shown, so that the total shunt capacitance is of the order of a half microfarad.

A pulse transformer 6 has line 3 in series with the primary 7 to ground, while secondary 8 is connected to the anode and the cathode of klystron V for the useful pulsed energization thereof. Ignitron switch tube V is connected across line 3 and primary 7 (in series) and serves to create a short across this circuit. This discharges the line through the primary of the transformer and through the switch tube and so produces the modulating pulse.

Ignitron V is ignited by the application of a considerable amount of power, such as two hundred amperes at two hundred volts. This power is supplied between terminal 11 and ground. Diode 12 is connected from igniter electrode 10 to ground to prevent a reverse potential upon the ignitor and possible damage thereto, as known.

The last, or gradient, grid of ignitron V is provided with a potential of the order of 10 kv. by the resistive voltage divider composed of resistors 14 and 15. These are connected in series between ground and the anode of V with the gradient grid connected to the junction between the two resistors.

The control grid of the ignitron is fired by a pulse of the order of 4 kv. and a current having an instantaneous value of several amperes. This pulse is applied between terminal 16 and ground. The same pulse, at reduced amplitude, is applied between terminal 17 and ground to the shield grid, which is seen to be connected directly to terminal 1'7 A source of repetitive deionizing pulses 19 is connected to the grid of triode V through grid-current-limiting resistor 20, which has a resistance of the order of one hundred ohms. The second terminal of source 19 is connected to the cathode of the triode and also to terminal 21, which is connected to a negative power source of the order of 2,000 volts.

The above circuit operates as follows. Assume that ignitron V has completed discharging the transmission line 3. A typical operation produces a 2.7 microsecond pulse; as determined by the discharge time of the line. The characteristic impedance of the line is a few ohms. A typical repetition interval between pulses is of the order of 2,700 microseconds. A deionization time of microseconds is characteristic of the ignitron with a large grid bias, and for that period of time the voltage at the anode of V should be zero.

This is brought about according to my invention by applying a pulse of 150 microsecond duration to the grid of triode V to allow the same to pass current. This is shown in FIG. 2 as pulse 25. This pulse starts at time T The typical duration thereof may be 150 microseconds, as for the type of apparatus herein described. This duration may be varied greatly as desired for other apparatus by altering the time constants of the circuit within source 19.

It will be recalled that the potential of the cathode of tube V is 2,000 volts negative. Thus the resting potential of 2,500 volts negative for the grid of V is sufiicient to 'cut that tube off during all periods of time except when pulse 25 is present. Pulse 25 has a positive'polarity and smears an amplitude of 700 volts. This causes the grid of triode V to go 200 volts positive with respect to the cathode and thus to cause the tube to act essentially as a short circuit from the anode of diode V to the 2,000 volt negative supply, or signal ground.

High voltage source 1 operates continuously and so current starts to build up through inductor 2 and triode V This is shown as the ramp function 26, which is the anode-cathode current of triode V in FIG. 2. In a representative apparatus, in which a Machlett 7003 triode 1 is employed, this current reaches 1.8 amperes by the time the rear of pulse 25 is reached.

The charged potential of ignitron V is twice that of high voltage supply I; i.c. it is 36 kv. When the line is discharged at time T this potential drops to zero. Because of the bypass type of short of V the voltage drop across inductor 2 makes up all of the potential of high voltage source 1 and the potential of the anode and of the gradient grid of V adjacent thereto is zero. This is shown in the lowest waveform of FIG. 2, at 27.

Upon the conclusion of the 156 microsecond interval, triode V becomes non-conducting and transmission line 3 starts to charge through inductor 2 and diode V However, the ionization within ignitron V has disappeared and although a positive potential be applied to the anode of that tube it will not conduct until triggered by a positive pulse on the control grid, etc., to repeat the cycle heretofore sketched. The potential at the anode of V increases according to a cosine function, as graphed in P16. 2. At the end of this increase shown, the potential has reached the full 36 kv. for this embodiment and the line remains charged until the next triggering pulse, which at 2,700 microseconds from the prior pulse, is a relatively long time away.

In the use of ignitron V it is necessary that the igniter pulse precede the general trigger pulse and the 150 microsecond pulse from source 19 (i.e., precede T by 40 microseconds. This is so that electron-emissive points will be formed in the mercury pool of the ignitron briefly in advance of need. This is standard practice for this tube and so is not illustrated. The pulse for the ignitor enters my apparatus at terminal 11, as has been described.

My system is relatively lossless, in that the energy stored in inductor 2. during the 150 microsecond interval is later returned to the line capacitors 5 as useful charging current after the 150 microsecond period has expired.

It will be understood that my invention can be carried out in a number of embodiments. However, I have employed a GE. 5233 ignitron for V and a thermionic high vacuum diode for V In one alternate embodiment, diode V is omitted and the former terminals thereof are connected by a wire. For this simplification the operating frequency (pulse repetition rate) must be nearly the same as the resonant charging period. This charging period is determined by the inductance of inductor 2 and the total network (line) capacitance. The latter is of the order of'a half microfarad and the former is 1.5 henries for an operating frequency of 360 pulses per second, which may be considered typical.

Not only do my hard tubes and circuit provide means for operating at very high powers that would otherwise not be attainable, but these provide apparatus of long life and stable operation at any power level.

Other alternate arrangements are also possible. All of the circuit to the right of V in FIG. 1 may have any configuration and serve any purpose as long as a high power pulse is required, there is a charge type of energy buildup and, of course, deionization protection to V is required. In the embodiment described the amplitude of the pulses out of secondary 8 of transformer 6 is 300 kilovolts.

It will be understood that the several tubes shown in FIG. 1 are preferably water cooled in high power embodiments, but this has not been shown. Also, the filament connections are conventional according to high power and high voltage practice and have not been shown.

The duration of the deionizing pulse may, of course, have any desired duration, depending upon the specific requirement in this regard of switch tube V Still other detailed modifications in the characteristics of the circuit elements, aspects of circuit connections and alteration of the coactive relation between the elements may be taken without departing from the scope of my invention.

Having thus fully described my invention and the manner in which it is to be practiced, I claim:

1. In an electrical modulator having pulse-forming means, and ionizable means for the actuation of said y pulse-forming means;

deionizing means comprising a single vacuum tube means connected to said ionizable means, control means to cause a flow of electrical energy in said vacuum tube means from said ionizable means, for longer than the duration of the pulse formed by said pulse-forming means, to thereby remove an ionizing potential from said ionizable means. 2. In a pulse modulator having electrical delay pulseforming means, with an ionizable shorting tube connected thereto,

the deionizing time of said shorting tube being in excess of the duration of the modulating pulse formed by said modulator;

means to deionize said shorting tube comprising only one vacuum tube having a current-flow electrode connected to said shorting tube,

means to cause current flow in said vacuum tube for at least the duration of said deionization time to remove voltage from said shorting tube by conducting a current flow from said shorting tube.

3. In a high power pulse modulator having an electrical delay line for forming a modulating pulse and a switch tube having an anode, said anode connected to said delay line, in which the deionization time of said switchtube is in excess of the duration of said modulating pulse; deionizing means comprising a single high vacuum tube connected to the anode circuit of said switch tube, pulse means connected to said high vacuum tube to cause a current flow in said high vacuum tube for the duration of said deionization time to remove ionizing potentials from said switch tube by current conduction from said anode circuit for the period of said deionization time.

4. In an electrical modulator having pulse-forming means, inductive charging means, and ionizable dischargng means connected to said pulse-forming means; deionizing means comprising a vacuum tube having an anode, a grid and a cathode, said anode connected to the junction between said inductive charging means and said pulse-forming means, pulse means connected to said grid to cause a current flow in said vacuum tube for the duration of the deionization time of said ionizable discharging means, to remove the ionizing voltage at said inductive 6 charging means from said ionizable discharging means for the duration of said deionization time.

5. In an apparatus having a load,

pulse-forming means connected to said load,

ionizable means connected to said pulse-forming means to actuate the same,

and reactive means connected to said pulse-forming means; means to deionize said ionizable means comprising a vacuum tube having electrodes, a current-passing electrode thereof connected only to said pulse-forming means and to said reactive means,

enabling means connected to another of said electrodes of said vacuum tube to cause said current-passing electrode to pass current,

said enabling means operative for an interval of time 5 sufliciently long to allow deionization of said ionizable means. 6. In a modulator having a load, a transmission line, means connecting said line to said load, an ionizab'le switch tube connected to said line to periodically discharge the same upon ionization of said switch tube,

and inductive means and thermionic means connected between an electrical energy supply and said line for the energization of said line;

means to deionize said switch tube comprising a triode vacuum tube having an anode, electron control means, and a cathode,

said anode directly connected to said inductive means and to said thermionic means,

a source of deionizing pulses,

said electron control means connected to said source of deionizing pulses,

said triode connected to bypass said electrical energy energization flowing through said inductive means in response to said deionizing pulses to allow deionization of said switch tube.

7. In a high power modulator having a load, an inductance-capacitance transmission line, a pulse transformer connecting said line to said load, a multiple grid metallic vapor switch tube connected to said line to said switch tube by a modulating pulse, and an inductor and a high vacuum diode connected in series between a positive voltage electrical energy supply and said line for charging said line; means to deionize said switch tube comprising, a high vacuum high power triode vacuum tube having an anode, a grid and a cathode, said anode connected to the junction between said inductor and said diode, a source of deionizing pulses having a duration at least an order of magnitude of time interval longer than the duration of the discharge pulse of said line through said switch tube, the grid of said triode connected to said source of deionizin-g pulses through a current-limiting resistor, and the cathode of said triode connected to a negative voltage electrical energy supply, said triode constituted and connected to bypass said charging current flowing through said inductor in response to said deionizing pulses for an interval of time sufficiently long to allow deionization of said switch tube, and not to bypass current at other times.

References Cited in the file of this patent UNITED STATES PATENTS Burlingame et al. Apr. 6, 1948 Van Dorsten Dec. 6, 1949 OTHER REFERENCES 

1. IN AN ELECTRICAL MODULATOR HAVING PULSE-FORMING MEANS, AND IONIZABLE MEANS FOR THE ACTUATION OF SAID PULSE-FORMING MEANS; DEIONIZING MEANS COMPRISING A SINGLE VACUUM TUBE MEANS CONNECTED TO SAID IONIZABLE MEANS, CONTROL MEANS TO CAUSE A FLOW OF ELECTRICAL ENERGY IN 